The term “compliant mechanisms” relates to a family of devices in which integrally formed flexural members provide motion through deflection. Such flexural members may therefore be used to replace conventional multi-part elements such as pin joints. Compliant mechanisms provide several benefits, including backlash-free, wear-free, and friction-free operation. Moreover, compliant mechanisms significantly reduce manufacturing time and cost. Compliant mechanisms can replace many conventional devices to improve functional characteristics and decrease manufacturing costs. Assembly may, in some cases, be obviated entirely because compliant structures often consist of a single piece of material.
In microelectromechanical systems (MEMS), compliant technology allows each mechanism of a MEMS system to be an integrally formed, single piece mechanism. Because MEMS devices are typically made by a layering and etching process, elements in different layers must normally be etched and formed separately from each other. Additionally, elements with complex shapes, such as pin joints, require multiple steps and layers to create the pin, the head, the pin-mounting joint, and the gap between the pin and the surrounding ring used to form the joint. Due to the limitations of the manufacturing processes involved, the resulting pin joint often will have excessive clearance between the shaft and the hole, thereby providing excessive slop in the joint.
An integrally formed compliant mechanism, on the other hand, may be constructed as a single piece, and may even be constructed in unitary fashion with other elements of the micromechanism. Substantially all elements of many compliant devices may be made from a single layer. Reducing the number of layers, in many cases, simplifies the manufacturing and design of MEMS devices. Compliant technology also has unique advantages in MEMS applications because compliant mechanisms can be manufactured unitarily, i.e., from a single continuous piece of material, using masking and etching procedures similar to those used to form semiconductors. In certain cases, semiconductors and associated MEMS devices may even be manufactured simultaneously on the same chip.
In MEMS as well as in other applications, there exists a need for “bistable devices,” or devices that can be selectively disposed in either of two different, stable configurations. Bistable devices can be used in a number of different mechanisms, including switches, valves, clasps, and closures. Switches, for example, often have two separate states: on and off. However, most conventional switches are constructed of rigid elements that are connected by hinges, and therefore do not obtain the benefits of compliant technology. Compliant bistable mechanisms have particular utility in a MEMS environment, in which electrical and/or mechanical switching at a microscopic level is desirable, and in which conventional methods used to assemble rigid body structures are ineffective.
Many mechanisms that are currently envisioned for applications such as microswitching are not truly bistable because they are not able to independently remain in two distinct positions. More precisely, such mechanisms often require the presence of a constant excitation voltage, or continuous pressure from an actuator, to keep them in one of the positions.
Furthermore, many known dual position MEMS devices have a displacement that is either too small or too large for a number of applications that require dual position motion. For example, it is desirable for a switch to have a displacement large enough to separate electrical conductors enough to ensure that arcing does not occur when the switch is open (i.e., in the “off” position). It is also desirable for the switch to have a displacement small enough to minimize the energy required to move the switch from one state to another. Many known devices do not provide sufficient electrical isolation when the switch is open, or require excessive voltage to operate. Many effective actuators have a comparatively small displacement, and are therefore incapable of moving a large displacement dual position mechanism without the use of some type of transmission. Often, bistable mechanisms often require a footprint that is excessive in relation to their displacement.
Yet further, known dual position MEMS devices typically require the use of multiple actuators. For example, many such devices require an actuator to move the device from a first position to a second position, and a second actuator to move the device from the second position back to the first position. The additional actuator requires processing time and space on the chip, thereby adding to the cost and volume of the microswitch.
Consequently, it would be an advancement in the art to provide a fully compliant MEMS device with true bistability, i.e., the ability to independently remain in either of two distinct positions. Furthermore, it would be an advancement in the art to provide a compact bistable MEMS device with a displacement that more closely corresponds with the specifications and requirements of microactuators and applications such as switching. Yet further, it would be an advancement in the art to provide a bistable MEMS device capable of independently moving from one position to another upon receipt of an electric signal.